The present invention relates to a method for preparation of a quaternary ammonium salt at high yield in a short reaction time.
Quaternary ammonium salts have been a remarkably important compound as starting materials for medicines and quasi-drugs and cosmetics, phase-transfer catalysts, ionized solvents, etc. Among the salts, quaternary pyridinium salts have recently be noticed mainly as an antibacterial agent and have been thought to increase its demand in future. However, it has been difficult to produce those compounds in an industrial scale at high efficacy in a short period of time. For instance, there has been disclosed a method comprising reacting dodecyl chloride with pyridine at 100xc2x0 C. for 24 hours in J. Chem. Soc., 682(1938) and a method comprising reacting an alkyl halide with 10 to 30% excess amount of pyridine at 60 to 130xc2x0 C. for 8 to 16 hours in J. Am. Chem. Soc. 68, 757-759(1946). However, in the former method, the reaction time is long and further yield of the object compound, a quaternary pyridinium salt, is such low as 1.7%, and in the latter method, the yield is considerably such high as 95% but the reaction time is remarkably long such as 8 to 16 hours, and therefore both methods are not satisfactory as a method for production of a quaternary ammonium salt in an industrial scale.
There has been also disclosed a method comprising reacting picoline, the methyl-substituted pyridine, with an alkyl halide under refluxing for 12 hours to obtain a quaternary picolinium salt in J. Heterocycl. Chem. 23(1)209-221(1986). However, the reaction time is so long, and thus this method is not satisfactory as a method for production of a quaternary picolinium salt in an industrial scale.
On the other side, a quaternary imidazolinium salt as well as a quaternary pyridinium salt have been thought to increase its demand in future, and there has been disclosed a method comprising reacting an alkyl halide with methyl imidazole under refluxing in an organic solvent to obtain a quaternary imidazolinium salt in Inorg. Chem. 35(5)1168-1178(1996). However, this method can not be easily conducted because of using a organic solvent and the yield is also low, and therefore this method is not satisfactory as a method for production of a quaternary imidazolinium salt in an industrial scale.
Furthermore, since a preparation for a quaternary ammonium salt as mentioned above have been conducted by batch process, its productivity is low and therefore those methods are not suitable for production in an industrial scale.
The present invention has been accomplished under such circumstances as above and its object is to provide a method for preparation of a quaternary ammonium salt by reacting a pyridine compound or an N-lower alkyl imidazole(hereinafter the pyridine compound and the N-lower alkyl imidazole are, sometimes, inclusively abbreviated as a heterocyclic compound of the present invention) with an alkyl halide in an industrial scale at high efficiency in a short reaction time.
The present invention relates to a method for preparation of a quaternary ammonium salt comprising reacting an alkyl halide with 2 equimolar amount or more per the alkyl halide of a pyridine compound or an N-lower alkyl imidazole at 120xc2x0 C. to 350xc2x0 C.
Further, the present invention relates to a method for the continuous production of a quaternary ammonium salt comprises introducing continuously an alkyl halide and 2 equimolar amount or more per the alkyl halide of a heterocyclic compound of the present invention into a pipe reactor from the one end thereof under heating at 120 to 350xc2x0 C. to pass through the pipe reactor wherein a reaction is allowed to take place, and taking out continuously the resulting quaternary ammonium salt from the other end of the reactor.
Namely, the present inventors have extensively conducted study in order to fulfill the above object to arrive at the finding that a quaternary ammonium salt can be produced effectively in a short reaction time by reacting an alkyl halide with 2 equimolar amount or more per the alkyl halide of a pyridine compound or an N-lower alkyl imidazole at 120xc2x0 C. to 350xc2x0 C., and the present invention has been completed on the basis of this finding.